Sort criteria does not work

Problem/Motivation

When using the sort criteria given in the example, the preview no longer works (after save) and when you test the view, the view crashes with the following error message:

The website encountered an unexpected error. Please try again later.
Error: Call to undefined function Drupal\views_birthday\Plugin\views\sort\drupal_get_user_timezone() in Drupal\views_birthday\Plugin\views\sort\Birthday->getOffset() (line 162 of modules\contrib\views_birthday\src\Plugin\views\sort\Birthday.php).
Drupal\views_birthday\Plugin\views\sort\Birthday->getOffset('', 'UTC') (Line: 120)
Drupal\views_birthday\Plugin\views\sort\Birthday->getNow() (Line: 96)
Drupal\views_birthday\Plugin\views\sort\Birthday->getDateField() (Line: 106)
Drupal\views_birthday\Plugin\views\sort\Birthday->getDateFormat('Ymd') (Line: 64)
Drupal\views\Plugin\views\sort\Date->query() (Line: 1373)
Drupal\views\ViewExecutable->_build('sort') (Line: 1289)
Drupal\views\ViewExecutable->build() (Line: 387)
Drupal\views\Plugin\views\display\PathPluginBase->execute() (Line: 180)
Drupal\views\Plugin\views\display\Page->execute() (Line: 1630)
Drupal\views\ViewExecutable->executeDisplay('page_1', Array) (Line: 77)
Drupal\views\Element\View::preRenderViewElement(Array)
call_user_func_array(Array, Array) (Line: 101)
Drupal\Core\Render\Renderer->doTrustedCallback(Array, Array, 'Render #pre_render callbacks must be methods of a class that implements \Drupal\Core\Security\TrustedCallbackInterface or be an anonymous function. The callback was %s.) (Line: 781)
Drupal\Core\Render\Renderer->doCallback('#pre_render', Array, Array) (Line: 372)
Drupal\Core\Render\Renderer->doRender(Array, ) (Line: 200)
Drupal\Core\Render\Renderer->render(Array, ) (Line: 241)
Drupal\Core\Render\MainContent\HtmlRenderer->Drupal\Core\Render\MainContent\{closure}() (Line: 573)
Drupal\Core\Render\Renderer->executeInRenderContext(Object, Object) (Line: 242)
Drupal\Core\Render\MainContent\HtmlRenderer->prepare(Array, Object, Object) (Line: 132)
Drupal\Core\Render\MainContent\HtmlRenderer->renderResponse(Array, Object, Object) (Line: 90)
Drupal\Core\EventSubscriber\MainContentViewSubscriber->onViewRenderArray(Object, 'kernel.view', Object)
call_user_func(Array, Object, 'kernel.view', Object) (Line: 142)
Drupal\Component\EventDispatcher\ContainerAwareEventDispatcher->dispatch(Object, 'kernel.view') (Line: 163)
Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object, 1) (Line: 80)
Symfony\Component\HttpKernel\HttpKernel->handle(Object, 1, 1) (Line: 57)
Drupal\Core\StackMiddleware\Session->handle(Object, 1, 1) (Line: 47)
Drupal\Core\StackMiddleware\KernelPreHandle->handle(Object, 1, 1) (Line: 106)
Drupal\page_cache\StackMiddleware\PageCache->pass(Object, 1, 1) (Line: 85)
Drupal\page_cache\StackMiddleware\PageCache->handle(Object, 1, 1) (Line: 47)
Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object, 1, 1) (Line: 52)
Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object, 1, 1) (Line: 23)
Stack\StackedHttpKernel->handle(Object, 1, 1) (Line: 706)
Drupal\Core\DrupalKernel->handle(Object) (Line: 19)

Steps to reproduce

Tested with Drupal 9.1.5 and German date formats e.g. d.m.Y
It may not work with all international date formats.

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes